The invention relates to a control technique for coping with undesired power supply abnormality in a semiconductor device or an electronic apparatus, and relates to, for example, a technique effective in a case of application to a liquid crystal display driver.
In case that an external power supply which is supplied to a drive-system semiconductor device such as a liquid crystal driver is cut off, the state of a driven device such as a liquid crystal display panel is required to be initialized until the semiconductor device is not able to operate. For example, in a case of a liquid crystal display driver, this is intended not to cause deterioration in characteristics or the like in liquid crystal display elements due to undesired charge information remaining in pixels of the liquid crystal display panel in case that an operation power supply is cut off. For this reason, an initialization process is performed which is called a display off-sequence process of discharging charge information of each pixel of the liquid crystal display panel, or the like. This process is, for example, a process of extracting held charges of each element by collectively selecting gate lines of the liquid crystal display panel and giving a predetermined potential to each source electrode, and the control thereof is performed by a logic circuit of a liquid crystal driver.
Normally, a liquid crystal driver receives a logic external power supply voltage from the outside and a drive power supply voltage having a level higher than that from an external power supply circuit. From such a relationship, it is possible to make it a start condition of a display off-sequence process that the drive external power supply voltage having a higher level is set to be at a predetermined level or lower. For example, in JP-A-2011-170349, the same process as the above is also performed.
Such a display off-sequence process is controlled by a logic circuit operating at a so-called logic voltage lower than a drive voltage. In JP-A-2014-010231, it has been considered that, even in case that the above response process is started on the basis of a drop in the voltage of a drive power supply, the response process may not be able to be completed due to a logic power supply dropping on the way or in advance. That is, the response process is started by detecting a drop in the voltage of the logic power supply. In JP-A-2014-202792, the response process is started in either case of a drop in the voltage of the drive power supply or a drop in the voltage of the logic power supply. In JP-A-2014-202792, it is considered that an operation power supply of a logic circuit is used for dropping the voltage of a drive power supply in case that the response process is started due to a drop in the voltage of the logic power supply.